Or the file didn't mention any real specifics about her rescue. Maybe just a ship name (IE - ...found by the U.S.S. XXX...")I'm guessing that he didn't read the entire file, since he was more than a bit annoyed that Admiral April forced him to come back.
He probably just glanced over it since it was actually part of the new recruits list that would be boarding the Enterprise.
There were probably more then a few names/entry's on that list.
Also, he wasn't aware that she would be his new Number One until Spock told him just as they arrived on the bridge.